prop tollerance

[Capt. Tobb]

I was taking part in the Christmas on the bayou back in Dec. and had a little problem. I was going in reverse so the judges could see the big marlin on the bow( only visible from stbd. side ) Stupid? YES! As my luck would have it, I met a log in the bayou in reverse.

(how about that shaft nut...nice!)

I have taken out the rudder( kinda looks like a pitching wedge ) and will take it to the machine shop monday. I came up with a "presidential solution" to measure the variation in the prop blades

It appears that one blade is out about 1/4" out and another is 1/8" out. I cruise at 26kts at 1850rpm, I am afraid that I know the answer to this question, is this variation acceptable?

 

[Finalee]

You might not feel it on a Hatt. (could not resist) Since the boat is out and from the looks of the rudder will be for a little while fix it and be done ! Vibrations where only good for The Beach Boys?

 

[garyd]

You can fix this yourself if ya have the patience and as big cresent wrench. That's how they fixed them for years including airplanes. I've done it so I know it is possible.

You have a good set up to check your results. Now go buy a large cresent wrench. Make sure the damage is to the blade that can be repaired. If the damage is to the hub you may not be experienced enough to fix it.

But if it just the outer edge of a blade it is real easy to fix and kinda fun. Sneak up on it. Use a grease pencil to figure out the area to repair then slowly use the large cresent wrench to bend back to the correct shape.

Make sure you slide the wrench all the way onto the blade. Spread the pressure do not locilize it or the jaws will create a crease/dimple. Slow and easy. You don't have much to move. A good prop guy could fix that in less than one hour, maybe like 10 minutes.

Have at it.

gayrd

 

[stormchaser]

Any one blade should be off no more than +/- 2% to be within spec of ISO 484 standard I (High accuracy) or 3% for standard II (medium accuracy). So .48"-.72" would be OK...the lower the better. That's for a 24" wheel, not sure what size ur running.

 

[captddis]

Old thinking is no more than 1/8 out on the blades. I want it better than that. It could be your shaft is out too, pull the prop and dial the shaft, then send the prop out.

 

[REBrueckner]

In the first photo it looks like your lock nut (the aft one) has a space....is it loose?

Also, and this is NOT a big deal, your nuts should be on in the reverse order...think one first, thick one last (aft)...

 

[Genesis]

Yep.

BTW the "current thinking" on props (and the guys with the machines to do 'em to "current thinking") make a HUGE difference in how the boat runs.

Find someone with the new fancy computer machine and take BOTH wheels over there. While you're at it have the shaft dialed.

You won't believe the difference.

I used to poo-poo the "computer prop guys" until I actually tried spending the extra money - one time. As soon as I came up on step after putting the reworked wheels back on the difference was INSTANTLY obvious.

 

[stormchaser]

I agree with the above totally. I had the prop on my trawler tuned by BlackDog props. They can get all the tolerances tighter than the ISO standard for high tolerance, but quite a bit. And it does make a BIG change. It actually increased speed for same RPM/Fuel Rate 15-20%...or allowed me to reduce fuel consumption from 2.5 down to 2 gph and maintain the same speed. Not sure the changes would be so drastic on a Hatt...this was on a pure displacement trawler with a single 130hp engine.

 

[Capt. Tobb]

Thanks guys, Nov 06 I took the main (better) and spare (cheaper chineese version) sets of wheels to the computer guy in Orange Beach, Tyler Delgren. I think he retired now but I am glad that I took them there, he was really informative. I guess I need to pull them and go to the place in Pensacola. As far as the nuts go, last time on the yard there were two old boat guys that almost got in to a fist fight over which nut goes where when I asked them. Considering that the little guy came loose, I think I will put him on first this time. Thanks again for the help...

 

[Genesis]

If you're in Pensacola the place is Accuprop. Awesome folks.

Good people - they know me. Tell 'em Karl says hi. (Don't know if it'll get you a better price or not.... )

Lap wheel to shaft, then remove and clean both taper and bore.

Make sure the keyway is clear and the key slides in with FINGER pressure when the prop is mounted before you tighten it up.

Little nut on first, torque to ~50% of final while tapping the prop's hub as it seats so as to make sure its on correctly.

Then big nut, torqued to 100%.

If you want to lock it put a bit of MarineTex (or plumber's epoxy putty) on the threads behind the nut when you're done. The cotter is to keep from losing the nuts, but if you tighten them properly and the shaft is lapped to the wheel it will not come off.

 

[Trojan]

If you're in Pensacola the place is Accuprop. Awesome folks.

Good people - they know me. Tell 'em Karl says hi. (Don't know if it'll get you a better price or not.... )

Lap wheel to shaft, then remove and clean both taper and bore.

Make sure the keyway is clear and the key slides in with FINGER pressure when the prop is mounted before you tighten it up.

Little nut on first, torque to ~50% of final while tapping the prop's hub as it seats so as to make sure its on correctly.

Then big nut, torqued to 100%.

If you want to lock it put a bit of MarineTex (or plumber's epoxy putty) on the threads behind the nut when you're done. The cotter is to keep from losing the nuts, but if you tighten them properly and the shaft is lapped to the wheel it will not come off.

Anyone that thinks they can do there own prop repair. Doesn't need a Hatteras. You may as well cut holes in the side of the boat and add oars. There is no comparison between a hammered prop and prop shop computer aided prop. The quality of work on your props is nothing but fantastic. I would never ever let a person hammer block my props. Your just wasting money and ruining your drive train. Karl is 100% correct.

BILL

 

[J's Dream]

I would never ever let a person hammer block my props.

Bill,

Could you tell me then how the computer shops rework the props? Everywhere I have ever seen hammers them or wrenches them...and then they are checked by the computer.

Jason

 

[Trojan]

Bill,

Could you tell me then how the computer shops rework the props? Everywhere I have ever seen hammers them or wrenches them...and then they are checked by the computer.

Jason

There not pounded against a formed block. There formed by hydrulic cylinders. Sure they use special hammers. but they are used in such a way that they reform the prop blades. The blades are also balanced differently. By using the computer each blade is the same. Pitch, size and smoothness. Something you can't do with hammer blocks. You can actually read each blade and know the exact pitch, height and smoothness. Hammer blocks only come close. Rebound from the steel block is enough to to change each blade. Also when using blocks nothing guarantees that the shaft taper is 90 degrees to the blades. If there using a computer program and a digital stylis for checking there not likely using hammer blocks.

BILL

 

[Genesis]

The place in Pensacola uses hydraulics along with the traditional tools.

They also have a high-speed balancing unit that they stick 'em on much like a high-speed tire balancer and work the balance as well.

You get back a printout with each wheel showing each blade when they're done.

These guys are GOOD. I thought it was crap (expensive crap at that) until I tried it. Never again do my wheels go to a hammer and block shop. Yeah, it costs more, but my experience is that you get more, so.....

BTW the guys at Accuprop won't charge you for a full rework if you don't need it. They're HONEST which is nice as well - they'll scan 'em and clean 'em up when they come in and if they're ok or just need a small amount of work or a balance that's all you pay for.

 

[garyd]

If no material was removed then balance isn't going to be effected if you get the blades straight (relatively since they have a curve to them)again. Since they are only out 1/4" to 1/8" you can certainly take them off and have them redynoed. Or you can do it yourself with excellent results.

It isn't that big a deal. I've fixed props that were curled and out over an inch. It appears that the rudder took the hit and the two blades that are out barely touched the log.

Do it yourself.

garyd

 

[stormchaser]

The props are actually within tolleraces for non-tuned straight from the factory props. I'd sorta question whether they actually hit the log or not... but either way...your best (but most expensive) alternative is taking them to a good computerized prop shop... at least that's what I would do...

 

[SKYCHENEY]

If you have a decent set of spares, throw those on so that you can get back in the water. Then take the old set to PropScan to get checked out. They will usually give you a report of the current condition along with recommendations for free. If they are not too bad, you could put them back on later or, depending on the price, have them tuned.